Cord Cedeno, a customer at the club, told MSNBC on Monday that Mateen tried to get in contact with him through Grindr

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The FBI is investigating whether gunman Omar Mateen visited Pulse nightclub and tried to communicate with some of its patrons on a gay dating app before killing 49 people and injuring scores at the Orlando club, authorities told NBC News.

Cord Cedeno, a customer at the club, told MSNBC on Monday that Mateen tried to get in contact with him through Grindr, a dating application for gay and bisexual men. Cedeno said he blocked Mateen "because he was creepy" and "recognized him off Grindr" after the rampage.

"That's not his first time there," Cedeno said. "He's been there several times. I know that for a fact."

An FBI official told NBC News that investigators are looking into similar reports.

'Like Firecrackers': Witness Recalls Orlando Gunfire

Anthony Kerney, who lives not far from the Pulse nightclub in Orlando, says he was sitting outside when he heard gunfire. He ran toward the club and began recording video of what he saw.